1. Field of the Invention
This invention relates to a process for selective formation of a deposited film, particularly to a selective formation process for forming a deposited film of a II-VI group compound in a self-alignment fashion.
The selective formation process of a deposited film according to the present invention is applicable for, for example, preparation of thin films to be used for semiconductor integrated circuits, optical integrated circuits, etc.
2. Related Background Art
FIGS. 1A-1E illustrate the steps of the process for forming a thin film by photolithography of the prior art.
First, a substrate 1 comprising a material species with uniform composition as shown in FIG. 1A is washed, and then a thin film 2 is deposited on the whole surface of the substrate 1 according to various thin film depositing methods (vacuum vapor deposition method, sputtering method, plasma discharging method, MBE method, CVD method, etc.) (FIG. 1B).
Subsequently, on the thin film 2 is applied a photoresist 3 (FIG. 1C), and the photoresist 3 is exposed to light by use of a photomask of a desired pattern and the photoresist 3 is removed partially by development (FIG. 1D).
With the remaining photoresist 3 as the mask, the thin film 2 is etched to form a thin film 2 with a desired pattern (FIG. 1E).
By repeating such photolithographic steps, thin films of desired patterns are laminated to constitute an integrated circuit. In that case, alignment between the thin films of the respective layers becomes an extremely important factor for the characteristics of the device. Particularly, in the case of ultra-LSI where precision of submicron is demanded, precision of the shape of thin films of the respective layers is also extremely important along with alignment.
However, in the above process for forming a thin film of the prior art, it is difficult to effect necessary alignment of the photomasks with good precision, and also the precision of shape is insufficient, because thin films of desired patterns are formed by etching.
FIGS. 2A-2D illustrate the steps of the process for forming a thin film by use of lift-off of the prior art.
First, a photoresist 4 is applied on a substrate 1 (FIG. 2A), and the photoresist 4 with a desired pattern is removed by photolithography (FIG. 2B).
Subsequently, a thin film 5 is deposited according to a thin film deposition method (FIG. 2C), and the remaining photoresist 4 is dissolved away. By this operation, the thin film on the remaining photoresist 4 is removed at the same time, whereby a thin film 5 with a desired pattern is formed. By repeating the above steps, an integrated circuit is constituted.
However, such a thin film forming process, because a thin film is formed on a photoresist, requires to perform deposition of a thin film at a temperature not higher than the resistant temperature of the photoresist, whereby the deposition method is greatly restricted. Also, in removing the photoresist, the shape of the remaining thin film is influenced thereby and therefore precision of the shape becomes insufficient. Also, there is also the problem that the side wall or the inner portion of the thin film may be highly probably contaminated with carbon, etc. which is the component of the photoresist, etc.
Also, as the selective deposition method, there has been known the method in which a monocrystal substrate is covered partially with an amorphous thin film, and the same material as the substrate material is epitaxially grown selectively only at the exposed portion of the monocrystal substrate. For example, there are the selective epitaxial growth (SEG) method in which a silicon monocrystal substrate is partially covered with silicon oxide to effect selective growth of silicon (B. D. Joyce & J. A. Baldrey, Nature vol. 195,485, 1962), the method in which a GaAs substrate is covered partially with an amorphous thin film such as SiO.sub.2, Si.sub.3 N.sub.4, etc. to effect selectively epitaxial growth of GaAs (P. Rai-Choudhury & D. K. Schroder, J. Electrochem. Soc., 118, 107, 1971), etc.
However, these selective deposition methods, because of growing selectively the monocrystal semiconductor of the same kind from the exposed surface of a monocrystal substrate, are limited in the deposition surface for the base to monocrystalline semiconductors, and therefore not applicable to polycrystalline substrates, or amorphous insulating substrates.
Thus, the deposited film forming method of the prior art is limited in available substrates, and further there are involved problems also in shape of the pattern, dimensional precision of the deposited film formed.